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Addictive/antisocial behaviours in Parkinson's are fundamentally underpinned by a 'motivated myopia'

Parkinson’s disease involves losing dopamine cells in a certain part of the brain. It makes sense, then, that dopamine medication is given to Parkinson’s patients to compensate for this loss of cells. The problem, though, is that the medication can bring about addictive behaviours (e.g., pathological gambling, hypersexuality, binge eating) in certain patients (about 1 in 7). What’s more, we still do not know how medication affects mental function to lead to these devastating side-effects. If we did, we would have more options to intervene and halt the development of addictive behaviours. We would also know, from a more scientific perspective, what dopamine is really doing in the brain when it comes to the ‘good stuff’ in life – is it acting as a kind of teaching signal, where it tells us something (like eating a sugary donut) is better or worse than expected? Is it conveying the undeniable sense of pleasure we get from things like eating sugary donuts? Or it is increasing our desire for certain things (like sugary donuts) and motivating us to go after them more often (even if we end up not liking them as much as we used to)?

My PhD research is focussed on uncovering the mental mechanisms underlying these addictive behaviours in Parkinson’s so I can help with developing treatment options, as well as answering this broader question about what dopamine does in the context of rewards. The first step I took in my research was looking at all the past studies in this area and formulating a model of what seems to be going in the mind of these patients with addictive behaviours. Following on from the work of others in the field, I developed a model I called ‘motivated myopia’, where these patients are hypermotivated to opt for short-term options (eating a pack of sugary donuts) at the expense of long-term, more beneficial options (maintaining a healthy weight). Happily, the model fits with a lot of what we know about dopamine functioning from other work and what we know the brain networks supporting motivation and choice.

I then sought to test my model. I ended up conducting the first multi-site, cross-national psychological study into addictive behaviours in Parkinson’s. I found support for the model and also found that it even explained, to some degree, antisocial behaviour (aggression and risky driving) that sometimes co-occurs in Parkinson’s patients with addictive behaviours. This was unexpected and exciting. I am now aiming to further develop this model.